System and method for image localization of effecters during a medical procedure

ABSTRACT

A computer-assisted imaging and localization system assists the physician in positioning implants and instruments into a patient&#39;s body. The system displays overlapping images—one image of the surgical site with the patient&#39;s anatomy and another image showing the implant(s) or instrument(s). The overlapping image of the implant/instrument is moved over the static image of the anatomy as the implant/instrument is moved. These moving image of the implant/instrument can be an unaltered image or an image altered to intensify or mitigate the anatomical or non-anatomical aspects of the moving image. Sliding these images over one another helps the surgeon in positioning devices or instruments with a high degree of accuracy and with a limited number of additional x-rays.

PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATIONS

This application is a utility filing from and claims priority toco-pending U.S. Provisional Application No. 62/336,999, entitled “Systemand Method for Image Localization of Effecters During a MedicalProcedure” filed on May 16, 2016, the entire disclosure of which isincorporated herein by reference. This application is also a utilityfiling from and claims priority to co-pending U.S. ProvisionalApplication No. 62/374,187, entitled “Detection of Tracked Metal ObjectsDuring Imaging”, filed on Aug. 12, 2016, the entire disclosure of whichis incorporated herein by reference.

BACKGROUND

Many surgical procedures require obtaining an image of the patient'sinternal body structure, such as organs and bones. In some procedures,the surgery is accomplished with the assistance of periodic images ofthe surgical site. Surgery can broadly mean any invasive testing orintervention performed by medical personnel, such as surgeons,interventional radiologists, cardiologists, pain management physicians,and the like. In surgeries and interventions that are in effect guidedby serial imaging, which we will refer to as image guided, frequentpatient images are necessary for the physician's proper placement ofsurgical instruments, be they catheters, needles, instruments orimplants, or performance of certain medical procedures. Fluoroscopy, orfluoro, is one form of intraoperative X-ray and is taken by a fluorounit, also known as a C-arm. The C-arm sends X-ray beams through apatient and takes a picture of the anatomy in that area, such asskeletal and vascular structure. It is, like any picture, atwo-dimensional (2D) image of a three-dimensional (3D) space. However,like any picture taken with a camera, key 3D info may be present in the2D image based on what is in front of what and how big one thing isrelative to another.

A DRR is a digital representation of an X-ray made by taking a CT scanof a patient and simulating taking X-rays from different angles anddistances. The result is that any possible X-ray that could be acquiredfor that patient can be simulated, which is unique and specific to howthe patient's anatomical features look relative to one another. Becausethe “scene” is controlled, namely by controlling the virtual location ofa C-Arm to the patient and the angle relative to one another, a picturecan be generated that should look like any X-ray taken in the operatingroom (OR).

Many imaging approaches, such as taking fluoro images, involve exposingthe patient to radiation, albeit in small doses. However, in these imageguided procedures, the number of small doses adds up so that the totalradiation exposure can be problematic not only to the patient but alsoto the surgeon or radiologist and others participating in the surgicalprocedure. There are various known ways to decrease the amount ofradiation exposure for a patient/surgeon when an image is taken, butthese approaches come at the cost of decreasing the resolution of theimage being obtained. For example, certain approaches use pulsed imagingas opposed to standard imaging, while other approaches involve manuallyaltering the exposure time or intensity. Narrowing the field of view canpotentially also decrease the area of radiation exposure and itsquantity (as well as alter the amount of radiation “scatter”) but againat the cost of lessening the information available to the surgeon whenmaking a medical decision. Collimators are available that can speciallyreduce the area of exposure to a selectable region. For instance, acollimator, such as the Model Series CM-1000 of Heustis Medical, isplaced in front of an x-ray source, such as the source 104 shown inFIG. 1. The collimator consists of a series of plates that absorb mostincident X-rays, such as lead. The only x-rays that reach the patientare those that pass through apertures between the plates. The positionof the plates can be controlled manually or automatically, and theplates may be configured to provide differently shaped fields, such amulti-sided field. Since the collimator specifically excludes certainareas of the patient from exposure to x-rays, no image is available inthose areas. The medical personnel thus have an incomplete view of thepatient, limited to the specifically selected area. Thus, while the useof a collimator reduces the radiation exposure to the patient, it comesat a cost of reducing the amount of information available to the medicalpersonnel.

A typical imaging system 100 is shown in FIG. 2. The imaging systemincludes a base unit 102 supporting a C-arm imaging device 103. TheC-arm includes a radiation source 104 that is positioned beneath thepatient P and that directs a radiation beam upward to the receiver 105.It is known that the radiation beam emanated from the source 104 isconical so that the field of exposure may be varied by moving the sourcecloser to or away from the patient. The source 104 may include acollimator that is configured to restrict the field of exposure. TheC-arm 103 may be rotated about the patient P in the direction of thearrow 108 for different viewing angles of the surgical site. In someinstances, radio-dense effecters, such as metal implants or instrumentsT, may be situated at the surgical site, necessitating a change inviewing angle for an unobstructed view of the site. Thus, the positionof the receiver relative to the patient, and more particularly relativeto the surgical site of interest, may change during a procedure asneeded by the surgeon or radiologist. Consequently, the receiver 105 mayinclude a tracking target 106 mounted thereto that allows tracking ofthe position of the C-arm using a tracking device 130. For instance, thetracking target 106 may include several infrared emitters spaced aroundthe target, while the tracking device is configured to triangulate theposition of the receiver 105 from the infrared signals emitted by theelement. The base unit 102 includes a control panel 110 through which aradiology technician can control the location of the C-arm, as well asthe radiation exposure. A typical control panel 110 thus permits thetechnician to “shoot a picture” of the surgical site at the surgeon'sdirection, control the radiation dose, and initiate a radiation pulseimage.

The receiver 105 of the C-arm 103 transmits image data to an imageprocessing device 122. The image processing device can include a digitalmemory associated therewith and a processor for executing digital andsoftware instructions. The image processing device may also incorporatea frame grabber that uses frame grabber technology to create a digitalimage or pixel-based image for projection as displays 123, 124 on adisplay device 126. The displays are positioned for interactive viewingby the surgeon during the procedure. The two displays may be used toshow images from two views, such as lateral and AP, or may show abaseline scan and a current scan of the surgical site. An input device125, such as a keyboard or a touch screen, can allow the surgeon toselect and manipulate the on-screen images. It is understood that theinput device may incorporate an array of keys or touch screen iconscorresponding to the various tasks and features implemented by the imageprocessing device 122. The image processing device includes a processorthat converts the image data obtained from the receiver 105 into adigital format. In some cases the C-arm may be operating in thecinematic exposure mode and generating many images each second. In thesecases, multiple images can be averaged together over a short time periodinto a single image to reduce motion artifacts and noise.

Standard X-ray guided surgery typically involves repeated x-rays of thesame or similar anatomy as an effecter (e.g.—screw, cannula, guidewire,instrument, etc.) is advanced into the body. This process of moving theeffecter and imaging is repeated until the desired location of theinstrument is achieved. This iterative process alone can increase thelifetime risk of cancer to the patient over 1% after a single x-rayintensive intervention.

Classic image guided surgery (“IGS”) uses prior imaging as a roadmap andprojects a virtual representation of the effecter onto virtualrepresentations of the anatomy. As the instrument is moved through thebody, the representation of the effecter is displayed on a computermonitor to aid in this positioning. The goal is to eliminate the needfor x-rays. Unfortunately, in practice, the reality of these devicesdoesn't live up to the desire. They typically take significant time toset-up, which not only limits adoption but only makes them impracticalfor longer surgeries. They become increasingly inaccurate over time asdrift and patient motion cause a disassociation between physical spaceand virtual space. Typical IGS techniques often alter work flow in asignificant manner and do not offer the physician the ability to confirmwhat is occurring in real-time and to adjust the instrument as needed,which is a primary reason fluoroscopy is used.

What would benefit greatly the medical community is a simple imagelocalizer system that helps to position instruments without alteringworkflow. It would be substantially beneficial if the system can quicklybe set-up and run, making it practical for all types of medicalinterventions both quick and protracted. The desirable system wouldsignificantly limit the number of x-rays taken, but does not requireeliminating them. Therefore, by both encouraging reimaging and usingthis as a means to recalibrate, the system would ensure that theprocedure progresses as planned and desired. Using the actual x-rayrepresentation of the effecter rather than a virtual representation ofit would further increase accuracy and minimize the need for humaninteraction with the computer. If the system mimics live fluoroscopybetween images, it would help to position instruments and provide theaccuracy of live imaging without the substantial radiation imparted byit.

SUMMARY OF THE DISCLOSURE

A computer-assisted imaging localization system is provided that assiststhe physician in positioning implants and instruments into a patient'sbody. The system has the desired effect of displaying the actualinstrument or implant and using this displayed to guide surgery withoutthe need to directly interact with the computer. The system does so bydisplaying and moving overlapping images on a computer screen, allowingone image to be seen through the other. These image “masks” can be theunaltered image or doctored images to intensify or mitigate theanatomical or non-anatomical aspects of the image. Sliding these imagesover one another can help to position medical devices with a high degreeof accuracy with a limited number of additional x-rays.

In another feature, a tracking element is provided that is mountable onthe shaft of an effecter. The tracking element includes marker bandsthat substantially encircle the effecter shaft that are configured forsensing by an optical tracking device. In one aspect, the configurationof one or more marker bands on the tracking element can provide indiciaof the nature of the effecter. This indicia can be used by the imageprocessing software to determine the nature of the displays and datamanipulation provided by the software.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of an image guided surgical setting includingan imaging system, an image processing device and a localizer ortracking device for surgical instruments and devices.

FIG. 2 is a diagram of steps in displaying movement of a trackedeffecter on an x-ray image of a surgical site.

FIGS. 3A-D are screen shots of image displays of a surgical site showingthe patient's anatomy and a movable image of a radio-dense effecter inrelation to a fixed image of the surgical site.

FIGS. 4A-C are screen shots of x-ray images of a surgical site andradio-dense effecter, including a low dose x-ray image and an image inwhich the display of the radio-dense effecter is enhanced relative tothe image of the anatomy.

FIGS. 5A-C are screen shots of x-ray images in which the radio-denseeffecter is represented by a metal mask in an image that moves relativeto the fixed image of the surgical site as the effecter moves.

FIGS. 6A-B are screen shots of x-ray images of the surgical site with anoverlaying metal mask image of the effecter.

FIG. 7 is a screen shot of an x-ray image with slugs indicating theposition of the tip of radio-dense effecters relative to the anatomyshown in the image.

FIG. 8 is a side view of a generic effecter having marker bands used fortracking the position of the effecter.

FIG. 9 is a side view of a generic effecter having a tracking elementmounted on the effecter and providing marker bands for tracking theposition of the effecter.

FIG. 10 is a side view of a generic effecter having another trackingelement mounted on the effecter and providing marker bands for trackingthe position of the effecter.

FIG. 11 is screen shot of an x-ray image of a surgical field with aneffecter and a region of interest within the viewing field.

FIGS. 12A-C are screen shots of low dose x-ray images showing images ofradio-dense effecters.

FIGS. 13A-F are screen shots of x-ray images of multiple radio-denseeffecters in a surgical field with images of the effecters isolated andrepresented by metal masks overlaid onto the image of the anatomy.

FIGS. 14A-E are a series of screen shots of an x-ray image in which theradio-dense effecters are automatically detected by the image processingdevice of the present disclosure.

FIG. 15A is a representation of a movement of the x-ray device or c-armduring a surgical procedure.

FIGS. 15B-D are screen shots of an x-ray image showing the movement ofthe image corresponding to the movement of the c-arm in FIG. 15A.

FIG. 16A is a representation of a movement of a radio-dense effecterduring a surgical procedure.

FIGS. 16B-C are screen shots of an x-ray image showing the movement ofthe image corresponding to the movement of the radio-dense effecter inFIG. 16A with the position of effecter remaining stationary.

FIG. 17A is a representation of a movement of a radio-dense effecterduring a surgical procedure.

FIGS. 17B-C are screen shots of an x-ray image showing the movement ofthe image corresponding to the movement of the radio-dense effecter inFIG. 16A with the position of the image of the anatomy remainingstationary.

FIG. 18A is a representation of a movement of a radio-dense effecterduring a surgical procedure.

FIGS. 18B-C are screen shots of an x-ray image showing the movement ofthe image corresponding to the movement of the radio-dense effecter inFIG. 18A with the position of effecter remaining stationary and withgrid lines superimposed on the image corresponding to the stationaryorientation of the effecter.

FIG. 19A is a representation of a movement of a radio-dense effecterduring a surgical procedure.

FIGS. 19B-C are screen shots of an x-ray image showing the movement ofthe image corresponding to the movement of the radio-dense effecter inFIG. 19A with the position of the image of the anatomy remainingstationary and with grid lines superimposed on the image correspondingto the different positions of the radio-dense effecter.

FIG. 20 are screen shots of x-ray images illustrating the low visibilityof certain radio-dense effecters in a surgical site.

FIG. 21 is a flow chart for detecting the presence and location of aradio-dense effecter in an image of a surgical site.

FIG. 22 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating one step of the detection method in the flow chart ofFIG. 21.

FIG. 23 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating a further step of the detection method in the flowchart of FIG. 21.

FIG. 24 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating another step of the detection method in the flow chartof FIG. 21.

FIG. 25 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating a subsequent step of the detection method in the flowchart of FIG. 21.

FIG. 26 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating yet another step of the detection method in the flowchart of FIG. 21.

FIG. 27 is a screen shot of an x-ray image of an effecter in a surgicalsite illustrating one step of the detection method in the flow chart ofFIG. 21.

FIG. 28 is a screen shot of an x-ray image of a surgical site in whichthe effecter has been detected and the metal mask of the effecterenhanced within the image.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the disclosure is therebyintended. It is further understood that the present disclosure includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles disclosed herein aswould normally occur to one skilled in the art to which this disclosurepertains.

According to one aspect of the invention, the process begins with takingan image of the anatomy to be addressed surgically. Typically this“localizing shot” or “baseline image” does not contain the radio-denseeffecter (e.g.—screw, cannula, guidewire, instrument, etc.) that is tobe moved/adjusted, although in one embodiment a single image containingthe effecter can be used. The image processing device 122 (FIG. 1)generates a digital image that can be displayed and manipulateddigitally. With the anatomy identified and displayed on a computerscreen, a “new” image with the effecter or instrument is taken, withthis image also converted to a digital image by the image processingdevice 122. This new image is displayed on top of the originallocalizing shot so that the resulting image looks like the conventionalimage on a fluoroscope screen, such as shown in FIG. 3A. In one aspectof the present disclosure, the effecter, such as effecter T in FIG. 1,incorporates a localizer system (e.g.—EM, Optical IGS, etc) capable oftracking movement of the effecter. The 3D movement of the effectermeasured by the localizer system can be applied to the digitalrepresentation of the “new” image relative to move the “new” imagerelative to the “localizing shot” image. Thus, as the tip of theeffecter is tracked, the movement of the “new” image shows the change inposition of the tip of the instrument being tracked relative to thestationary anatomy depicted in the “localizing shot”. On the computerscreen, it thus appears as if live fluoroscopy is being taken as theeffecter is being moved and as if the actual tool or implant is beingmoved and adjusted relative to the patient's anatomy. When the nextimage is taken, the tip of the effecter is at the location that thephysician desires. It can be appreciated that unlike the typical IGSsystem in which a digital model of the effecter is manipulated, thesystem and method of the present disclosure relies on manipulating anactual image of the effecter in the surgical field.

The movement of the “new” image on the display is based on the geometryof the tip of the effecter relative to the location within the cone beamof the fluoroscope, as depicted in FIG. 2. The nearer the tip of thetracked effecter is to the x-ray source, for the same relative movement,the greater the movement of the “new” image and therefore the effecter'sprojection (in pixels) relative to the size of the “localizing shot”.Assuming a standard size image, such as a 9 in. image intensifier, andassuming a typical 1000 mm separation of the x-ray source from theintensifier, there is an approximate 2.24 pixel per mm movement of thetracked effecter projected on the image intensifier. Away from the imageintensifier and closer to the source, this pixel-per-mm movement ratiois magnified in a consistent manner as shown in FIG. 2. In particular,the movement distance of the projection of the tracked effecter on theimage intensifier is given by Y′=X′*Y/X, where Y is the actual movementdistance of the effecter, X is the distance from the source to thetracked effecter/instrument, X′ is the distance from the source to thelocalizing image at the image intensifier and Y′ is the projectedmovement distance. It can be appreciated that the distance X′ istypically fixed throughout the procedure for a conventional C-arm X-raysource. The distance X and the movement distance Y can be determined bythe image processing device 122 (FIG. 1) based on data received from thelocalizer system used to track the movement of the effecter. The imageprocessing device uses the projected movement distance Y′ to move the“new” image accordingly on the display.

The “new” image, shown in the lower representation in FIG. 2, can betaken using standard x-ray settings, or may be taken using less thanfull dose radiation or low dose settings which has the benefit ofblurring out the anatomy while having relatively little impact on theimage of an effecter in the image. (It is understood that a“radio-dense” material generally does not allow the imaging rays orx-rays to pass through so that the radio-dense effecter blocks theunderlying anatomy). When the “new” image is a low dose image, the “new”image can be combined with or overlaid on the image from the localizingshot allowing the user to see the resulting combined image with theappearance of the anatomy appearing as a live fluoroscopic image. Theresult is an image as seen in FIG. 3A that can help guide an effecter tothe correct location desired by the physician.

In the example shown in FIGS. 3A-D, a bone screw 10 to be tracked isintroduced into a patient after an initial “localizing shot” andprojected on the display 122/123 (FIG. 1) as the screen shot of FIG. 3A.As the tracked instrument 10 is moved out of the field of the localizingshot or baseline image 12, as depicted in the screen shot of FIG. 3B,the two overlapping images can be appreciated, with the localizing shot12 seen to the left and the new low radiation image 14 to the right. Itcan be noted that the metal screw in the low radiation image is veryprominent while the representation of the anatomy is obscure. When thetracked screw is moved into an ideal location based on the desire of thephysician, such as shown in the screen shot of FIG. 3C, the image on thescreen can constantly project a combined image (overlaying the full doselocalizing shot with the low dose image) that replicates what a newfluoroscopic image would look like at any point, mimicking livefluoroscopy without obtaining a new live image. It can be appreciatedthat the localizing or baseline image 12 does not change as the effecter10 is moved, at least so long as the C-arm or X-ray source is not moved.Thus, the digital data for the localizing image 12 is not manipulated bythe image processing device during movement of the effecter. On theother hand, the image processing device does manipulate the digital dataof the “new” image based on the projected movement of the trackedeffecter so that the “new” image moves across the display as theeffecter is moved.

A stationary full dose new image can be taken, such as the display inthe screen shot of FIG. 3D, to confirm that the effecter 10 is in thelocation desired by the physician. If for some reason the imagealignment is off or further fine tuning is required, this newly acquiredimage can replace the prior localizing shot image as the baseline image,and the process is repeated. The system thus resets or recalibrates whenthe full dose new image is taken, so that subsequent images are alwaysmore accurately displayed than previous ones.

It can be appreciated that as the physician moves the effecter 10 thelow dose image moves with the effecter. When the effecter is within thefield of the baseline or localizing shot image, as in FIG. 3C, the imageof the effecter from the low dose image is combined with the stationarylocalizing image so that the physician can clearly see the patient'sanatomy and the effecter's position relative to that anatomy. As theeffecter is moved within the field of the baseline image, the image ofthe effecter (and the “new” image) moves accordingly so that thephysician can guide the tip of the effecter to the desired position inthe anatomy. It is contemplated that the overlaid images can be in twodisplays with two views of the surgical site, such as an AP view and alateral view, for instance. The baseline and subsequent new images canbe acquired as both AP and lateral views. As the effecter is moved, itsassociated image is moved in both displayed views so that the surgeoncan observe the 3D movement of the effecter.

In recognition that a new image is not actually being acquired duringeach step of movement of the effecter, the physician can acquire new lowdose images at various stages of movement of the effecter to verify theactual location of the effecter. Thus, any error in the actual vs.displayed position of the effecter relative to the anatomy is eliminatedwith each new low dose image taken. In other words, with each low doseimage, the system recalibrates the actual position of the effecterrelative to the anatomy based on the digital data acquired from the lowdose image. The new data identifying the new position of the effecter isthen the starting point for movement of the new image as the effecter ismoved by the surgeon. It is contemplated that the physician may requiremultiple low dose images as the effecter is moved into its finalposition, with each low dose image recalibrating the actual position ofthe effecter, potentially culminating in a full dose image to verify thefinal position.

Although a low radiation image is shown in FIGS. 3A-D, a conventional orfull dose “new” image can be taken and displayed with similar results,as shown in the screen shot of FIG. 4A. A low radiation image can beused, as see in the screen shot of FIG. 4B, or a metal intensificationof the “new” image can be performed as shown in the screen shot of FIG.4C. The image of FIG. 4B is obtained under low radiation so that theanatomic features are effectively washed out. While the image of theeffecter 10 is also washed out due to the low dosage, the metal or otherradio-dense material is sufficiently radiopaque so that the resultingimage of the effecter in FIG. 3B is still outstanding enough to beeasily seen.

The image of FIG. 4C is generated by intensifying the pixels associatedwith the image of the effecter 10, so that when the full image isdisplayed the image of the effecter essentially washes out the image ofthe underlying anatomy. In either case, what is projected has theability to “fool the eye” to make it appear to the surgeon as if theinstrument is moving under live fluoroscopy.

The metal intensification image of FIG. 4C can constitute a metal maskapplied to the images, such as the image in the screen shot of FIG. 5A.As shown in FIG. 5B, the image of the effecter 10 is represented by agreen mask 20 overlaying the actual image. The movement of the mask iscorrelated to the actual movement of the effecter as determined by thelocalizer. When the green layer of the mask 20 is moved to a more ideallocation, a confirmatory x-ray can be taken as in the screen shot ofFIG. 5C. The green or metal mask 20 can be generated by the imageprocessing device 122 (FIG. 1) using software that examines the pixelsof the image to determine which pixels are associated with anatomicfeatures and non anatomic features based primarily on the intensityvalue of each pixel. Various filters can be applied each pixel of thedigitized X-ray image to enhance the edges between pixels representinganatomic and non-anatomic features. Once the pixels associated with thenon-anatomic features are acquired and the edges enhanced, the pixelsoutside the selected non-anatomic pixels can be washed out, leaving onlythe pixels for the non-anatomic feature corresponding to the effecter.

Similar to the images of FIGS. 5A-C, image tracking can be applied inFIGS. 6A_B to a Jamshedi needle 10′ that is repositioned to a desiredposition in the patient's body. However, in FIG. 6A there is no initial“localizing shot”. The “new” image serves as both the stationary and themoved image. The image of the effecter is replaced by a green layermask, such as the mask 20 of FIG. 5C, and just the green layer of theimage is moved on the background of the “new” image. The image guidancesystem of the effecter can determine the relative location of theinstrument in the image, so that rather than moving the entire image asin the prior examples, only a narrow area around the region of theeffecter 10′ is moved.

The present invention contemplates a system and method for moving imagemasks or overlapping image sets based on the movement of a trackedobject, which provides the physician or surgeon with the ability toplace a surgical effecter at the correct location inside a patient witha minimal number of X-ray images. Movement projection is not based onthe absolute motion of the effecter but rather on the relative motion ofthe tracked effecter within the imaging space. Although knowledge of theabsolute location of the tip of the effecter is needed for certain imagemovements, such as shown in FIG. 6B, such knowledge is not necessary. Itis only necessary to know the relative motion between the originalposition and the new position of the effecter, and the distance from thetip of the effecter/instrument to the X-ray source.

The position of the effecter/instrument can be recalibrated on each newX-ray shot. On the instrument side this means that each x-ray resets therelative position or the initial starting point of the “new” image tothe current location of the tracked effecter to which is linked a “new”image with that effecter in it. This feature makes the system mostlyfocused on relative movement so that the potential time horizon fordrift to set in is minimized.

The system and method disclosed herein creates “pseudo-livefluoroscopy”, meaning that the physician/surgeon can see the movement ofthe effecter/instrument in real-time without constant imaging of thepatient. The present disclosure further contemplates automating takingimages to create constantly re-updated spot images with “pseudo-livefluoroscopy” in between to create a continuous high accuracy instrumenttracking device with a live fluoroscopy appearance with dramaticallyfewer images and resulting radiation. The methods of the presentdisclosure only require knowledge of relative movement (meaning thedelta between the last position of the instrument to the current) andonly require displaying the 2D motion of the effecter/“new” image tomake this functional. The present disclosure provides a morecomprehensive imaging system compared to typical IGS where it isnecessary to know the absolute movement and the actual knowledge of whatis being moved (in order to project a correct virtual representation ofit).

The system and method of the present invention works with a metal maskor an actual image, and can work with low dose images or full doseimages. With this system, the entire image can be moved or adjusted, asshown in FIGS. 3, 4, or only a region of interest is moved or adjusted,as shown in FIG. 6B.

The system and method disclosed herein uses the actual effecter (or morespecifically an active x-ray picture of the effecter), not a virtualrepresentation of it as in a typical IGS. This approach makes itpossible to emphasize or deemphasize different features (e.g.—anatomy,metal, etc) of the two images to aid in visualization. The methodsdisclosed herein do not require distortion correction or dewarping, or acalibration phantom, as is often required in typical IGS. Thus, thepresent system does not require a grid on the c-arm to correct for thevarious types of distortion (i.e.—pin cushion, etc.). When an IGS systemis being used, the present system permits the IGS tracker to be eitherplaced at the tip of the effecter (in the case of an EM microsensor orthe like) or projected to the tip by a known offset that is more typicalof an optical system. The present system does not require any patientreference, such as a “beacon” that is standard on nearly all IGSsystems. In particular, it is not necessary to know the location of theobject's tip relative to the c-arm (the distance of the tip between theimage intensifier and the x-ray source) and the in plane movement(distance and trajectory) of the effecter

The present system and method can operate with a single image,separating metal or other radio-dense material from anatomy and leavingthe anatomy without the metal or other radio-dense material as a layer,or the metal or other radio-dense material can be moved without anatomyas a layer, as depicted in FIGS. 5, 6, or the layers can be moved in anycombination.

The present method and system even works with distorted IGS data (likeis classically a problem with EM), as the movement won't be perfect butwill asymptotically get closer to the correct position. For instance, ifthe IGS data is inaccurate by 20%, then after the first movement, a“new” x-ray will confirm that it is 20% off. However, the system is thenrecalibrated so that now moving the new “new” image is not only moreaccurate, but the distance needed to move is only 115^(th) the priordistance. Thus, even if the system still has a 20% error, the nextmovement to close the gap of this 20% will be only 4% off (i.e., 20% of20%). The use of relative motion and this perpetually smaller distancemoved between each x-ray allows the present system to use noisy warpedEM data for application in the OR.

In another feature, the tip of the effecter, such as effecter 10, can berepresented on the displayed x-ray image as a slug 30 shown in thescreen shot of FIG. 7. The position of the slug can correspond to theposition of the tip of the effecter relative to the anatomy and can takevarious forms, including a circle or bulls-eye and an arrow, as depictedin FIG. 7. The appearance of the slug 30 can be varied to signifydifferent conditions in the process of navigating the effecter to thedesired anatomical position. For instance, the size or configuration ofthe slug can be indicative of the degree of accuracy associated with theparticular movement. For example, the slug can be depicted as a circlewhen the accuracy is lower and an arrow when the accuracy is greater.The size of the circle can be related to the degree of accuracy for thelocation of the tip of the effecter.

The color of the slug can be also varied to indicate certain conditions,namely conditions of the C-arm or x-ray device. For example, the slugcan be green if the current position of the C-arm is within a narrowrange of its position, 2 mm for instance, when the localizing image wasacquired, and red if the current position is outside that range. Whenthe slug changes from green to red the physician can obtain a new x-rayimage to establish a new baseline and verify the actual current positionof the effecter. As long as the color of the effecter remains green thephysician can have confidence that the actual location of the effectertip corresponds to the displayed location. As an alternative to changingcolor, the slug 30 can flash if the position of the C-arm has changed.

In the case where multiple effecters are present in a surgical site, thecolor of the slug 30 can be indicative of the particular effecterassociated therewith. It should be appreciated that all of the stepsdiscussed above can be implemented for multiple effectors for accuratenavigation of the effecters to a desired position. It can be expectedthat the multiple effecters may require positioning and re-positioningduring a procedure, so methods of the present disclosure can be modifiedaccordingly to account for multiple effecters and multiple slugs.

In another embodiment, a slug 35, shown in FIG. 7, marking the locationof the tip of the effecter can include a central element 36, in the formof a dot or small circle, corresponding to the position of the tip, anda second element 37, in the form of a circle that is at least initiallyconcentrically disposed around the central element 36. The secondelement in the form of a circle can correspond to a point on theeffecter offset along the longitudinal axis of the effecter from thetip. The location of the second element or circle 37 relative to thecentral element or dot 36 provides the physician with an indication ofthe attitude of the effecter. In the depiction of FIG. 7, the offset ofthe circle 37 relative to the dot 36 indicates that the shaft of theassociated effecter extends to the left and downward in the surgicalfield.

In an alternative embodiment, a slug 35′ can include the same firstelement in the form of a dot or small circle 36′ depicting the positionof the effecter tip, as shown in FIG. 7. However, rather than include acircle for the second element, the second element of the slug 35′ is an“I” that not only indicates the orientation of the effecter relative toits tip, but also indicates the rotation about the axis of the effecter.The angular offset of the “I” from a vertical orientation provides thesurgeon with a visual indication of the rotational orientation of theimplant, tool or instrument.

As discussed above, the present systems and methods utilize trackinginformation from a localizer system that acquires the position of theeffecter. Typical localizer systems utilize an array of optical sensorsto track an optical tracking component mounted to the end of theeffecter. This arrangement is cumbersome and often interferes with thesurgeon's field of view of the surgical site. In one aspect of thepresent disclosure, an effecter 40 includes a handle 41 with anelongated shaft 42 terminating in a working tip 43, as depicted in FIG.8. The shaft 42 is provided with optically trackable markers 44 a, 44 bin the form of optical bands that at least partially encircle the shaft.It is contemplated that the bands encircle at least 300° around theshaft so that the markers are visible at all rotational angles of theeffecter. The bands may be formed by optical tape applied to theeffecter or may be applied directly to the material of the effecter,such as by etching. The two markers 44 a, 44 b permit tracking themovement of the effecter in five degrees of freedom—X, Y, Z, pitch (Xrotation) and yaw (Y rotation). The markers 44 a, 44 b are provided at apredetermined distance from the working tip 43 so that the localizersoftware can use the detected location of the two markers to extrapolatethe 5 DOF position of the working tip.

In one aspect of this feature of the invention, the markers 44 a, 44 bare separated by a predetermined spacing in which the spacing isindicative of the type of effecter. For instance, one spacing of themarkers may denote a cage inserter while another different spacing ofthe markers may denote a distracter. The localizer system can beconfigured to discern the spacing of the markers 44 a, 44 b and thenrefer to a stored data base to determine the nature of the effecterbeing detected. The data base includes information locating the workingtip in relation to the markers so that the position of the working tipcan be accurately determined by sensing the location of the markers. Thedata base may also include a model of the instrument that can be used togenerate the metal mask 20 described above. Once the particular effecteris identified, the localizer system will always know where the workingtip is located even when one of the two markers is obscured.Alternatively, the width of one or more of the bands may be indicativeof the nature of the effecter being detected.

In another aspect, the markers are incorporated into a tracking element45 that can be mounted to the shaft 42′ of a tool 40′ that is otherwisesimilar to the tool 40, as shown in FIG. 9. The tacking element includesa cylindrical or partially cylindrical body 46 that can be clipped ontothe shaft 42′ and held in position with a friction grip. The cylindricalbody 46 includes the two markers 44 a′, 44 b′ in the form of bands thatencircle the body. A third marker 44 c′ can be provided on an arm 48that projects from the cylindrical body, with the third markerconstituting an optically detectable band. The addition of the thirdmarker 44 c′ adds a sixth degree of freedom to the position datadetected by the localizer device, namely roll or rotation about theZ-axis or longitudinal axis of the shaft 42′. The bands 44 a′, 44 b′ canbe spaced apart in the manner described above to denote a particulareffecter.

In an alternative embodiment, an effecter 40″ shown in FIG. 10 includesan existing conventional fiducial marker 44 a″ on the shaft 42″ of theeffecter. A tracking element 45″ includes a cylindrical or partiallycylindrical body 46″ configured to be clamped onto the shaft 42″ of theeffecter. The body 46″ includes a second marker 44 b″ in the form of aband that encircles the cylindrical body, and may include a third marker44 c″ on a perpendicular extension 48″. The two markers 44 b″, 44 c″ onthe tracking element 45″ cooperate with the existing fiducial 44 a″ onthe effecter to permit detecting the position of the effecter, andtherefore the working tip 43″, in six degrees of freedom. In thisembodiment, the tracking element 45″ is clamped to the shaft 42″ at aparticular height h relative to the working tip 43″. The height hproduces a predetermined spacing relative existing fiducial 44 a″, whichspacing can be used to identify the nature of the particular effecter. Acalibration tool may be used to position the tracking element 45″ at theproper height for a particular effecter.

As mentioned, the location of the markers on the effecter can be used toidentify the nature of the effecter—i.e., as a tool, instrument, implantetc. The imaging software remembers what effecters are in the surgicalfield as well as the positions as they are moved within that field. Evenif one of more of the markers are temporarily blocked from view of thelocalizer or tracking device, the imaging software can extrapolate theposition of the effecter based on the position of the available markers.

In a further aspect of the invention, the image processing software canbe configured to automate certain features of the system based on thetype of effecter detected and the nature of the procedure. The softwarecan permit the surgeon to identify the nature of the surgical procedure,and then this information together with the information regarding theeffecter or effecters in use can be used to toggle certain displayfeatures. The toggled features can include metal enhancement (asdiscussed herein), the nature of the slugs displayed on the x-ray image,or the use of one or two adjacent views (such as AP and lateral at thesame time).

The system described above provides a method for tracking an effecter,such as a tool T within a displayed field F, as illustrated in FIG. 11.The present disclosure further contemplates imaging software implementedby the image processing device 22 (FIG. 1) that is activated only whenthe tracked radio-dense object, such as tool T, enters the surgicalfield F and a new image has been taken by the radiologist or surgeon.When these two conditions occur, an object mask for the tool, such asthe green mask 20, is displayed and the image may be manipulated by thesurgeon based on manipulations of the effecter or other radio-denseobject. The software remains activated until a new image is taken thatdoes not include the tracked instrument. If the radio-dense objectreappears in the field F, the software remembers the original locationof the field and the tool and allows manipulation by the radiologist orsurgeon.

The software of the present disclosure thus provides a metalidentification feature that is always running in the background of theimaging software execution. The software automatically identifies thepresence of a radio-dense object in the surgical field without anyoperator intervention, and displays an image of the radio-dense objectwithout operator intervention. The present disclosure thus contemplatesa system for identifying a radio-dense object in an image field andenhancing the display of that object for the benefit of the surgeonattempting to navigate the object within the surgical field. Thesoftware disclosed herein thus identifies the nature and parameters ofthe radio-dense object without any input or intervention from theradiologist or surgeon. The software analyzes the x-ray image to locatethe radio-dense object or objects and then create a mask correspondingto the configuration of the object. When the object is moved, thesoftware can move only the object mask without modifying the underlyingimage of the surgical field. In one approach, the software utilizesexisting tracking data for the guided surgical tool to identify theregion of the image field in which the tip of the instrument or tool canbe found, and/or a general angle of projection of the tool on the x-rayobtained from the existing tracking data. The present disclosure thusprovides a system that can locate a tool T even where the tracking dataonly identifies a region R within the viewing field F (FIG. 11).

Once the radio-dense object is located, the software and system of thepresent disclosure enhances or intensifies the image of the radio-denseobject. As shown in FIG. 12A, some radio-dense objects M are difficultto see in a low dose image. As shown FIG. 12C, the problem isexacerbated when the low dose image is merged with a prior standard doseimage (FIG. 12B), such as according to the techniques described U.S.Pat. No. 8,526,700, which issued on Sep. 3, 2013, the entire disclosureof which is incorporated herein by reference. The present disclosurecontemplates software executed by the image processing device 122(FIG. 1) that identifies the location of the radio-dense object(s) M,even in an image field as shown in FIG. 12A, and then intensifies theradio-dense objects M′ in a composite image shown in FIG. 12C so thatthe radio-dense objects are sufficiently visible to the surgeon. Thesoftware can locate the radio-dense object directly from the image FIG.12A, or can use angle of projection and/or location data provided by animage guidance component, to speed up the process of identifying thelocation of the radio-dense object(s) M. The system and softwaredisclosed herein thus provides means for locating and enhancingincredibly faint objects within the viewing field, even when the imageis a low dose image. Once the radio-dense object(s) M′ are located andenhanced, only the enhanced radio-dense object is moved while theunderlying baseline or composite x-ray image can remain stationary sinceonly the object is being tracked. It is further contemplated that thetracked objects can be limited to only select ones of the radio-denseobjects that may appear in a particular field of view. The non-trackedradio-dense objects can remain un-enhanced and left stationary even asthe image moves with the tracked radio-dense objects M′. Moreover, anyone or multiples of radio-dense objects in an image can be identified,enhanced and moved independently as independent masks overlying abaseline or composite x-ray image. With this feature, multiplephysicians can work simultaneously and together to position radio-denseobjects necessary for the surgical procedure, all working from the sameunderlying stationary baseline or composite x-ray image.

The system and software of the present disclosure allows isolation of aradio-dense object within an image, such as the image FIG. 13A and theisolated image in FIG. 13B. The isolated image can be used to guidemovement of the radio-dense object which can then be reintegrated withthe x-ray image at a new location as shown in FIG. 13C. This process canbe performed with any radio-dense object, once it has been identified,as illustrated in FIGS. 13D-F. The radio-dense objects can berepresented by a mask, with the masks for multiple objects beingcolor-coded, as shown in FIG. 13F.

FIGS. 14A-F shows a series of screen shots of displays generated by thepresent system and software. The first image in FIG. 14A, shows a faintobject M in a low radiation image. It is apparent from this image thatthe radio-dense object M is too faint for a surgeon to reliablymanipulate the instrument or tool. In the composite image of FIG. 14Bthe radio-dense object is even fainter. FIG. 14C shows an image of onestep in the metal identification algorithm implemented by the softwareof the present disclosure which relies on identifying linear edges thatare indicative of a non-anatomic feature. When tracking information forthe particular effecter or object is added, as shown in FIG. 14D, thecorrect linear edge is identified as the radio-dense object, which isthen enhanced and displayed in the image of FIG. 14E.

The system and software further provides two ways to view movement of atracked radio-dense object within a surgical field. The system describedin U.S. Pat. No. 8,526,700, incorporated by reference above, provides asystem for orienting a view as the x-ray device or C-arm is angled, asdepicted in FIG. 15A. In this system, when the C-arm is moved fromposition 1 to position 2, the displayed images move from the position inFIG. 15B to the position shown in FIG. 15C. In FIG. 15D, grid lines areadded that can ultimately be used to orient the C-arm to a perfectalignment for a Ferguson (flat endplate) view of a spinal field from theorthogonal x-ray image. The grid lines are parallel to the orientationof the effecter or radio-dense object.

In accordance with the present disclosure, when the radio-dense effecteror tool is moved, as shown in FIGS. 16-17, the tracked object controlsthe angle of the displayed image. The tracked object shown in FIG. 16Ais maintained in a constant orientation (such as vertical in FIG. 16B)and the x-ray image itself is rotated commensurate with the movement ofthe tracked object, as shown in FIG. 16C. It can be appreciated that thechange in angular orientation of the image between FIG. 16b and FIG. 16Cis the same as the change in angular orientation of the effecter fromposition 1 to position 2 in FIG. 16A.

As an adjunct to this feature, the image data for the rotated image ofFIG. 16C can be used to identify a movement for the c-arm to produce adesired shot of the effecter and the surgical site. For instance, theimage data can be used to identify a movement angle for the c-arm togenerate an en face view down the shaft of the effecter. Similarly, theimage data can be used to center the c-arm over the shaft of theeffecter or angle the c-arm to shoot perpendicular to the effecter shaftand centered over the tip of the instrument.

Alternatively, as shown in FIGS. 17A-C, the x-ray image can remainstationary while the image or mask of the tracked radio-dense object ismoved commensurate with the actual movement of the tracked radio-denseobject. The depth of the radio-dense object can be further adjusted bymoving the metal mask or image axially along its length. The grid linescan be added to the displays, whether the tracked object remainsstationary in the field of view, as in FIGS. 18A-C, or the x-ray viewremains stationary and the image or mask of the effecter is moved, as inFIGS. 19A-C.

The grid lines can help illustrate angular movements of the effecterprojected into the particular imaging plane (e.g., AP or lateral). As analternative or adjunct, the display of the image of the moving effectercan be manipulated according to the nature of the movement. When theeffecter, or more specifically the tip of the effecter, is moved in anorthogonal direction (x, y, z) the image of the effecter moves linearly.When the effecter is rotated or pivoted relative to the anatomy, theimage of the effecter can be skewed in relation to the angle of pivot.Thus, as the effecter pivots in one plane, an image of the effecter in aperpendicular plane skews as the effecter pivots, and more particularlythe diameter in the direction of pivoting can shrink and expand as theeffecter pivots.

As described above, the imaging software of the present systemimplements a method to detect the presence and location of trackedradio-dense objects and enhances the objects. The position andorientation of the radio-dense effecter, such as a tool or instrument,in space with respect to an X-ray device are measured by a tracker orlocalizer system associated with the effecter. This tracking informationis used to translate an X-ray image of the effecter on the viewingscreen that predicts where the effecter would appear if another X-rayimage were acquired. The image of the tool can be merged with apreviously acquired image of the patient's anatomy, with the previouslyacquired image remaining static. The resulting merged image informs thephysician about the placement of the effecter relative to the anatomy.

One problem with this approach is that certain commonly used surgicaltools T can be difficult to see in an X-ray image, especially if thisimage was acquired at a low X-ray dosage, as depicted in the screen shotimages of FIG. 20. The visibility of the surgical tool is furtherdiminished by the merging of a baseline image with a subsequent low doseimage. Consequently, the present disclosure contemplates a method forenhancing the visibility of a tracked surgical tool in a merged X-rayimage.

The steps of one method implemented by the imaging software are shown inthe chart of FIG. 21. Several parameters are available to optimize themethod for particular classes of surgical tools. All steps have beendesigned to be straightforward to implement on a graphics processingunit, such as the GPU of the image processing device 122 (FIG. 1), whichperforms optimally when the same computational operation can beperformed at all pixels in an image simultaneously. In the presentimplementation, the entire operation can be applied to a standard sizeimage in half a second with a consumer-grade graphics card, whichsuffices for most usage patterns.

One step of the method is to detect rectangles within the x-ray image.Each pixel is assigned a score that represents how well a darkrectangular pattern can be fitted to the neighborhood centered on thepixel. A rectangle is defined by its angle, width, and length. The scorefor a particular rectangle is the sum of the differences in theintensity values between points along the inside of the long edges ofthe rectangle and points along the outside (FIG. 22). This scorecalculation is performed for many different possible rectangles over arange of angles, widths, and lengths, and the highest score is reported,along with the corresponding angle, width, and length.

When tracking a radio-dense tool that is especially thick, thedifference calculation can also be performed at multiple depths in theinterior of the rectangle. This ensures that the rectangle has ahomogeneous interior. The intensity difference formula can be clamped toa narrow range of possible values, and scaled by a fractional exponent,so that especially large intensity differences will not have adisproportionate influence on the final score.

In a next step, pixels of the x-ray image are assigned to therectangles. This step extends the results from rectangle detection. Foreach pixel, the neighborhood around the pixel is searched for thehighest-scoring rectangle that overlaps it (FIG. 23). This score isreported, along with the corresponding angle, width, and length. Thisstep is needed because rectangles have corners and intersections, andthe pixels at these locations are not centered on the rectangle thatbest contains them.

In an X-ray image, a surgical tool may comprise multiple connectedrectangles, so it is preferable to join the multiple rectangles togetherinto a single contiguous region. In order to determine whether or notpixels belong to the same region, for two adjacent pixels, each of whichhas been assigned a rectangle score, angle, width, and length from theprevious steps, the connection criterion is the sum of the differencesin the rectangle scores, angles, widths, and lengths (FIG. 24). If theconnection criterion falls below a threshold, the pixels share aconnection. The relative contributions of the scores, angle, widths, andlengths can be weighted in order to control their influence on thecriterion. Each pixel has 8 neighbors to which it might potentially beconnected. This operation is performed at each pixel for all 8directions. To reduce computation time, connections between pixels withvery low rectangle scores can be ignored.

In the next step the tracking information obtained from the localizer ortracking device for the tool is related to the pixels. The trackingdevice provides data for the position and orientation of the tip of thesurgical tool in space. This tip can be virtually projected onto thesurface of the X-ray camera and related to a point and an angle withinthe X-ray image, as described above. For enhancement purposes, theprimary interest is in rectangular image features that have a positionand angle that are close to the projected tool tip. For each pixel, thedistance to the projected tool tip is calculated, and the differencebetween the angle of the tool tip and the angle of the rectangle at thepixel is calculated. These values can be clamped and scaled with anexponent to yield weights that quantify the spatial proximity andangular proximity of the pixel to the tool tip (FIG. 25). A tool istypically a long thin object, and pixels behind the tip belong to theobject while pixels in front of the tip do not. This prior knowledge canbe encoded by including orientation information into the calculation ofspatial proximity.

The pixels are then grouped into contiguous regions. Each region willhave a unique index, a rectangle score, a spatial proximity, and anangle proximity. These values will be accessible at each pixel in theregion. There are various algorithms available for this task. Thealgorithm used here was chosen because it can be performed at each pixelin parallel. The region growing algorithm proceeds iteratively. At eachiteration, for each of 8 possible directions, each pixel looks at itsneighbor in that direction. If the pixel shares a connection with itsneighbor, then they compare rectangle scores. If the neighbor has ahigher score, then the pixel receives the score and the index of itsneighbor. Otherwise, if the scores are equal, and the neighbor has ahigher index, then the pixel receives the index of its neighbor. If thepixel shares a connection with its neighbor and the neighbor has ahigher spatial proximity, then the pixel receives the spatial proximityof its neighbor. If the pixel shares a connection with its neighbor andthe neighbor has a higher angular proximity, then the pixel receives theangular proximity of its neighbor. At the end of the iteration, if theindex, score, spatial proximity or angular proximity have changed forany pixel in the image, then another iteration is performed. Otherwise,the algorithm halts.

When the algorithm has finished, each pixel has been assigned to aregion. Each region has a unique index, and each region has the bestrectangle score, spatial proximity, and angular proximity out of all thepixels in the region. These values are stored at each pixel in theregion.

Next, the regions are visually enhanced. In an X-ray image, a surgicaltool should appear darker than the surrounding area. To enhancevisibility, the pixels inside the region can be made darker, and thepixels outside the region lighter (FIG. 26). The changes to intensityshould be smooth so that no spurious textures are introduced into theimage, and so that the enhancement is robust in the presence ofpotential errors from the previous steps. Each pixel looks at each otherpixel in the neighborhood. The score, angle, width, and length of therectangle centered at the neighbor are found, as well as the score,spatial proximity, and angular proximity of the region to which theneighbor belongs.

The latitudinal and longitudinal axes of the neighboring rectangle aredetermined. The distance between the pixel and its neighbor is expressedas a sum of a latitudinal component and a longitudinal component. Thelatitudinal component is passed to a difference-of-Gaussians model thatreturns a negative value for pixels within the interior of the rectangleand a positive value in the exterior. The longitudinal component ispassed to a hyperbolic model that returns a fraction that approaches 0as the longitudinal distance grows. The offset to the pixel contributedby this neighbor is a product of the rectangle score, region score,spatial proximity, angular proximity, latitudinal weight, andlongitudinal weight. The offsets from all neighboring pixels are addedtogether. This step yields an intensity offset that can be used in theimage merging step.

The tracking information is then used to isolate the region of interest.The tracking information is used to weight the regions according totheir proximity to the tool tip. This will generate a mask that can beused to selectively weight different parts of the image when the imageis merged (FIG. 27). For each pixel, the mask value is the product ofthe region score, spatial proximity, and angle proximity. This value canbe thresholded and scaled with an exponent to suppress irrelevantregions of the image. The edges of the regions are often jagged and donot exactly correspond to the tool. It is thus necessary to expand theregion and smooth the boundaries so that the final merged image will nothave any visually unpleasant discontinuities. We accomplish this withmorphological dilation, followed by convolution with a Gaussian kernel.The values of the pixels in the mask are clamped to between 0 and 1. Avalue of 0 indicates that the pixel does not belong to the region ofinterest; a value of 1 indicates that the pixel fully belongs to theregion of interest. In the next step, the entire tool image is enhanced.The intensity offset image is added to the original image of the tool.The resulting sum may now have pixels outside the acceptable intensityrange of 0 to 255. To bring the intensities back to an acceptable range,and to further improve the contrast around the edges of the radio-densematerial, the histogram of the intensities within the mask region of theimage sum is constructed in order to determine low and high quantiles.All intensities in the sum are scaled linearly so that the low quantileis now 0 and the high quantile is now 255. This yields an enhanced toolimage.

Finally, the enhanced tool image is added to the anatomical image. Atpixels where the mask value is high, the enhanced tool imagepredominates, while at pixels where the mask value is low, theanatomical image predominates. The maximum and minimum ratios of the twoimages are chosen so that neither image is ever completely suppressed.This final merged image is displayed to the user as depicted in thescreen shot of FIG. 28.

The present disclosure should be considered as illustrative and notrestrictive in character. It is understood that only certain embodimentshave been presented and that all changes, modifications and furtherapplications that come within the spirit of the disclosure are desiredto be protected.

What is claimed is:
 1. A method for generating a display of an image ofa patient's internal anatomy and of radio-dense effecter in a surgicalfield during a medical procedure, comprising: acquiring a baseline imageof the surgical field including the patient's anatomy; acquiring animage of the radio-dense effecter in the surgical field; overlaying theimage of the radio-dense effecter on the baseline image of the surgicalfield with the image of the radio-dense effecter positioned relative tothe image of the patient's anatomy in the same manner as the actualradio-dense effecter is positioned relative to the actual anatomy;tracking the movement of the radio-dense effecter; and displaying theoverlaid images with the image of the radio-dense effecter moving inaccordance with the tracked movement of the radio-dense effecter.
 2. Themethod of claim 1, wherein the image of the radio-dense effecter isacquired from the baseline image.
 3. The method of claim 1, wherein: thebaseline image is acquired as a full dose x-ray image of the patient'sanatomy; and the image of the radio-dense effecter is acquired from aless than full dose x-ray image of the patient's anatomy with theradio-dense effecter in an initial position relative to the anatomy. 4.The method of claim 1, further comprising: acquiring a new image of theeffecter in the surgical field after the effecter has been movedrelative to the anatomy; subsequently overlaying the new image of theeffecter relative to the baseline image as the radio-dense effecter issubsequently moved relative to the anatomy.
 5. The method of claim 1,wherein the step of acquiring an image of the radio-dense effecter inthe surgical field includes altering the image.
 6. The method of claim5, wherein the step of altering the image of the radio-dense effecter inthe surgical field includes enhancing the specific image of the effecteritself.
 7. The method of claim 5, wherein the step of altering the imageof the radio-dense effecter in the surgical field includes reducing theintensity of the specific image of the anatomy relative to the intensityof the specific image of the radio-dense effecter.
 8. The method ofclaim 5, wherein the step of altering the image of the radio-denseeffecter includes replacing the image of the actual effecter in thesurgical field with a mask of the radio-dense effecter.
 9. The method ofclaim 5, wherein the step of altering the image of the radio-denseeffecter includes generating an image of a slug indicative of theworking tip of the radio-dense effecter.
 10. The method of claim 9,wherein the configuration of the image of the slug changes if theimaging device used to acquire the baseline image is moved.
 11. Themethod of claim 9, wherein: the image of the slug includes a centralelement and a second element representing a point on the radio-denseeffecter offset from the working tip along a longitudinal axis of theradio-dense effecter; and the orientation of the second element relativeto the central element is based on the angular orientation of theradio-dense effecter relative to the surgical field.
 12. The method ofclaim 11, wherein the central element is a dot or a small circle and thesecond element is a larger concentric circle.
 13. The method of claim11, wherein the central element is a dot or a small circle and thesecond element is a non-circular element adapted to represent a rotationof the radio-dense effecter about its longitudinal axis.
 14. A systemfor displaying of an image of a patient's internal anatomy and ofradio-dense effecter in a surgical field during a medical procedure,comprising: a device for acquiring images of the surgical field; atracking device for tracking the position of the radio-dense effecterwithin the surgical field; an image processor for receiving data fromthe device for acquiring images and from the tracking device, the imageprocessor including a memory and a computer processor for processing thedata and to generate data corresponding to a baseline image of thesurgical field and an image of the radio-dense effecter in the surgicalfield, the processor operable to execute software to overlay the imageof the radio-dense effecter on the baseline image of the surgical fieldwith the image of the radio-dense effecter positioned relative to theimage of the patient's anatomy in the same manner as the actualradio-dense effecter is positioned relative to the actual anatomy, thesoftware further operable to move the image of the radio-dense effecterrelative to the baseline image as the effecter is moved relative to theactual anatomy; and a display for receiving data from the imageprocessor to display the overlaid images.
 15. A tracking element for asurgical tool or instrument having an elongated shaft and a working tip,the tracking element comprising: a cylindrical body configured to clamponto the elongated shaft of the tool or instrument; at least oneconcentric band at least partially encircling the outside surface of thecylindrical body, the at least one concentric band adapted to bedetected by an optical localizer or an optical detection deviceassociated with an x-ray imaging system.
 16. The tracking element ofclaim 15, wherein the at least one concentric band is an optical tapeapplied to the outside surface of the body.
 17. The tracking element ofclaim 15, further comprising at least two concentric bands on theoutside surface of the cylindrical body, wherein the at least twoconcentric bands are positioned apart at a predetermined distanceindicative of the type of tool or instrument.
 18. The tracking elementof claim 15 wherein the at least one concentric band has a band widththat is indicative of the type of tool or instrument.
 19. The trackingelement of claim 15, further comprising an arm projecting outward fromsaid cylindrical body and including a band on the outside surface of thearm adapted to be detected by an optical localizer or optical detectiondevice.